/*
  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  Copyright (C) 2004-2023 The Stockfish developers (see AUTHORS file)

  Stockfish is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  Stockfish is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "thread.h"

#include <algorithm>
#include <cassert>
#include <cstdlib>
#include <deque>
#include <initializer_list>
#include <map>
#include <memory>
#include <utility>

#include "evaluate.h"
#include "misc.h"
#include "movegen.h"
#include "search.h"
#include "tt.h"
#include "uci.h"

namespace Stockfish {

ThreadPool Threads;  // Global object


// Constructor launches the thread and waits until it goes to sleep
// in idle_loop(). Note that 'searching' and 'exit' should be already set.
Thread::Thread(size_t n) :
    idx(n),
    stdThread(&Thread::idle_loop, this) {

    wait_for_search_finished();
}


// Destructor wakes up the thread in idle_loop() and waits
// for its termination. Thread should be already waiting.
Thread::~Thread() {

    assert(!searching);

    exit = true;
    start_searching();
    stdThread.join();
}


// Reset histories, usually before a new game
void Thread::clear() {

    counterMoves.fill(MOVE_NONE);
    mainHistory.fill(0);
    captureHistory.fill(0);
    pawnHistory.fill(0);

    for (bool inCheck : {false, true})
        for (StatsType c : {NoCaptures, Captures})
            for (auto& to : continuationHistory[inCheck][c])
                for (auto& h : to)
                    h->fill(-71);
}


// Wakes up the thread that will start the search
void Thread::start_searching() {
    mutex.lock();
    searching = true;
    mutex.unlock();   // Unlock before notifying saves a few CPU-cycles
    cv.notify_one();  // Wake up the thread in idle_loop()
}


// Blocks on the condition variable
// until the thread has finished searching.
void Thread::wait_for_search_finished() {

    std::unique_lock<std::mutex> lk(mutex);
    cv.wait(lk, [&] { return !searching; });
}


// Thread gets parked here, blocked on the
// condition variable, when it has no work to do.
void Thread::idle_loop() {

    // If OS already scheduled us on a different group than 0 then don't overwrite
    // the choice, eventually we are one of many one-threaded processes running on
    // some Windows NUMA hardware, for instance in fishtest. To make it simple,
    // just check if running threads are below a threshold, in this case all this
    // NUMA machinery is not needed.
    if (Options["Threads"] > 8)
        WinProcGroup::bindThisThread(idx);

    while (true)
    {
        std::unique_lock<std::mutex> lk(mutex);
        searching = false;
        cv.notify_one();  // Wake up anyone waiting for search finished
        cv.wait(lk, [&] { return searching; });

        if (exit)
            return;

        lk.unlock();

        search();
    }
}

// Creates/destroys threads to match the requested number.
// Created and launched threads will immediately go to sleep in idle_loop.
// Upon resizing, threads are recreated to allow for binding if necessary.
void ThreadPool::set(size_t requested) {

    if (threads.size() > 0)  // destroy any existing thread(s)
    {
        main()->wait_for_search_finished();

        while (threads.size() > 0)
            delete threads.back(), threads.pop_back();
    }

    if (requested > 0)  // create new thread(s)
    {
        threads.push_back(new MainThread(0));

        while (threads.size() < requested)
            threads.push_back(new Thread(threads.size()));
        clear();

        // Reallocate the hash with the new threadpool size
        TT.resize(size_t(Options["Hash"]));

        // Init thread number dependent search params.
        Search::init();
    }
}


// Sets threadPool data to initial values
void ThreadPool::clear() {

    for (Thread* th : threads)
        th->clear();

    main()->callsCnt                 = 0;
    main()->bestPreviousScore        = VALUE_INFINITE;
    main()->bestPreviousAverageScore = VALUE_INFINITE;
    main()->previousTimeReduction    = 1.0;
}


// Wakes up main thread waiting in idle_loop() and
// returns immediately. Main thread will wake up other threads and start the search.
void ThreadPool::start_thinking(Position&                 pos,
                                StateListPtr&             states,
                                const Search::LimitsType& limits,
                                bool                      ponderMode) {

    main()->wait_for_search_finished();

    main()->stopOnPonderhit = stop = false;
    increaseDepth                  = true;
    main()->ponder                 = ponderMode;
    Search::Limits                 = limits;
    Search::RootMoves rootMoves;

    for (const auto& m : MoveList<LEGAL>(pos))
        if (limits.searchmoves.empty()
            || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), m))
            rootMoves.emplace_back(m);

    // After ownership transfer 'states' becomes empty, so if we stop the search
    // and call 'go' again without setting a new position states.get() == nullptr.
    assert(states.get() || setupStates.get());

    if (states.get())
        setupStates = std::move(states);  // Ownership transfer, states is now empty

    // We use Position::set() to set root position across threads. But there are
    // some StateInfo fields (previous, pliesFromNull, capturedPiece) that cannot
    // be deduced from a fen string, so set() clears them and they are set from
    // setupStates->back() later. The rootState is per thread, earlier states are shared
    // since they are read-only.
    for (Thread* th : threads)
    {
        th->nodes = th->tbHits = th->nmpMinPly = th->bestMoveChanges = 0;
        th->rootDepth = th->completedDepth = 0;
        th->rootMoves                      = rootMoves;
        th->rootPos.set(pos, &th->rootState, th);
        th->rootState      = setupStates->back();
        th->rootSimpleEval = Eval::simple_eval(pos, pos.side_to_move());
    }

    main()->start_searching();
}

Thread* ThreadPool::get_best_thread() const {

    Thread*                 bestThread = threads.front();
    std::map<Move, int64_t> votes;
    Value                   minScore = VALUE_NONE;

    // Find minimum score of all threads
    for (Thread* th : threads)
        minScore = std::min(minScore, th->rootMoves[0].score);

    // Vote according to score and depth, and select the best thread
    auto thread_value = [minScore](Thread* th) {
        return (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
    };

    for (Thread* th : threads)
        votes[th->rootMoves[0].pv[0]] += thread_value(th);

    for (Thread* th : threads)
        if (abs(bestThread->rootMoves[0].score) >= VALUE_MATE_IN_MAX_PLY)
        {
            // Make sure we pick the shortest mate / stave off mate the longest
            if (th->rootMoves[0].score > bestThread->rootMoves[0].score)
                bestThread = th;
        }
        else if (th->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY
                 || (th->rootMoves[0].score > VALUE_MATED_IN_MAX_PLY
                     && (votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]]
                         || (votes[th->rootMoves[0].pv[0]] == votes[bestThread->rootMoves[0].pv[0]]
                             && thread_value(th) * int(th->rootMoves[0].pv.size() > 2)
                                  > thread_value(bestThread)
                                      * int(bestThread->rootMoves[0].pv.size() > 2)))))
            bestThread = th;

    return bestThread;
}


// Start non-main threads

void ThreadPool::start_searching() {

    for (Thread* th : threads)
        if (th != threads.front())
            th->start_searching();
}


// Wait for non-main threads

void ThreadPool::wait_for_search_finished() const {

    for (Thread* th : threads)
        if (th != threads.front())
            th->wait_for_search_finished();
}

}  // namespace Stockfish
